N-in-1 dosing pharmacokinetics in drug discovery: experience, theoretical and practical considerations

N-in-1 (or cassette) dosing pharmacokinetics (PK) has been used in drug discovery for rapid assessment of PK properties of new chemical entities. However, because of potential for drug-drug interactions this procedure is still controversial. This study was to retrospectively evaluate the N-in-1 dosing approach in drug discovery with an emphasis on the potential for drug-drug interactions. The systemic clearance, volume of distribution, oral bioavailability, and renal excretion of the 31 lead compounds in rats, dogs or chimpanzees were significantly correlated between the N-in-1 dosing and discrete studies with r values of 0.69, 0.91, 0.53, and 0.83 (p < 0.005 for all), respectively. PK parameters for 11 quality control compounds which were involved in 194 N-in-1 studies for screening approximately 1000 compounds had coefficient of variations of less than 70%. The intrinsic microsomal clearances generated from the N-in-1 and discrete incubations were nearly identical (r = 0.97, p < 0.0001). The intrinsic clearances of quality control compound from the N-in-1 incubations were consistent with its discrete CL(int) estimate (cv: 5.4%). Therefore, N-in-1 dosing is a useful approach in drug discovery to quickly obtain initial PK estimates. Potential drug-drug interactions that result in confounding PK estimates do not occur as frequently as expected.

Pharmacokinetics and pharmacodynamics of DPC 333 ((2R)-2-((3R)-3-amino-3{4-[2-methyl-4-quinolinyl) methoxy] phenyl}-2-oxopyrrolidinyl)-N-hydroxy-4-methylpentanamide)), a potent and selective inhibitor of tumor necrosis factor alpha-converting enzyme in rodents, dogs, chimpanzees, and humans

DPC 333 ((2R)-2-((3R)-3-amino-3{4-[2-methyl-4-quinolinyl) methoxy] phenyl}-2-oxopyrrolidinyl)-N-hydroxy-4-methylpentanamide)) is a potent and selective inhibitor of tumor necrosis factor (TNF)-alpha-converting enzyme (TACE). It significantly inhibits lipopolysaccharide-induced soluble TNF-alpha production in blood from rodents, chimpanzee, and human, with IC(50) values ranging from 17 to 100 nM. In rodent models of endotoxemia, DPC 333 inhibited the production of TNF-alpha in a dose-dependent manner, with an oral ED(50) ranging from 1.1 to 6.1 mg/kg. Oral dosing of DPC 333 at 5.5 mg/kg daily for 2 weeks in a rat collagen antibody-induced arthritis model suppressed the maximal response by approximately 50%. DPC 333 was distributed widely to tissues including the synovium, the site of action for antiarthritic drugs. Pharmacokinetic and pharmacodynamic studies in chimpanzee revealed a systemic clearance of 0.4 l/h/kg, a V(ss) of 0.6 l/kg, an oral bioavailability of 17%, and an ex vivo IC(50) for the suppression of TNF-alpha production of 55 nM (n = 1). In a phase I clinical trial with male volunteers after single escalating doses of oral DPC 333, the terminal half-life was between 3 and 6 h and the ex vivo IC(50) for suppressing TNF-alpha production was 113 nM. Measurement of the suppression of TNF-alpha production ex vivo may serve as a good biomarker in evaluating the therapeutic efficacy of TACE inhibitors. Overall, the pharmacological profiles of DPC 333 support the notion that suppression of TNF-alpha with TACE inhibitors like DPC 333 may provide a novel approach in the treatment of various inflammatory diseases including rheumatoid arthritis, via control of excessive TNF-alpha production.

Use of CT scan in the diagnosis of pediatric acute appendicitis

BACKGROUND

The efficacy of CT scan in the diagnosis of pediatric appendicitis has hot been established.

METHODS

Every patient under the age of 18 who was diagnosed and treated for acute appendicitis in the 1 year period from March 1998-March 1999 at Lakeland Regional Medical Center were included. The presentation, laboratory evaluation, imaging evaluation, hospital course, and pathologic evaluation were reviewed. Selected imaging studies were reviewed by an independent radiologist.

RESULTS

Forty-six patients were treated for appendicitis; 17 of them received CT scans (37%). The CT scans predicted appendicitis in 9 of 17 cases (sensitivity = 53%). False-negative studies resulted in some morbidity but no mortality. The radiology review indicated that three cases clearly did not demonstrate appendicitis. The other false-negative studies were secondary to either technical or professional factors.

CONCLUSION

The efficacy of CT imaging in the diagnosis of acute appendicitis in children has still not been demonstrated. This limited series indicates that if CT scanning is to be used in pediatric patients, more attention to technical and professional factors may be required. Some of these factors, particularly the ingestion of oral contrast, are particularly problematic in small children and may limit the effectiveness of this modality.

Determination of DuP 128, an ACAT inhibitor and its sulphoxide and sulphone metabolites in human plasma by liquid chromatography

A sensitive and specific high-performance liquid chromatographic (HPLC) method with fluorescence detection was developed for the simultaneous determination of DuP 128 (N'-(2,4-difluorophenyl)-N-[5-(4,5-diphenyl-1H-imidazol-2-ylthio)p entyl]-N- hepthylurea), an ACAT inhibitor, its sulphone metabolite (XB277), and the separate determination of sulphoxide metabolite (XC164) in human plasma. After deproteinizing plasma samples with acetonitrile, the organic layer, created by adding approximately 0.25 g of NaCl, was removed, evaporated to dryness, and the residue then reconstituted with 400 microliters of acetonitrile. The acetonitrile layer was washed with 5 ml of hexane and then 50 microliters was injected into the HPLC. DuP 128 and XB277 were simultaneously quantified using a YMC basic column and fluorescence detection (lambda Ex = 270 nm and lambda Em = 385 nm). XC164 was quantified using a Waters microBondpack C18 reversed-phase column and fluorescence detection (lambda Ex = 270 nm and lambda Em = 365 nm). The relationship between the peak height and plasma concentrations best fit a power curve and showed an average correlation coefficient of > 0.99 over a concentration range of 1-200 ng ml-1 for DuP 128 and XC164 and 2.5-200 ng ml-1 for XB277. Good intraday and interday assay precisions (RSD < 10%) and accuracy (< 14%) for all three compounds were observed. The methods were sufficiently sensitive and selective to quantify plasma concentrations of DuP 128 and its sulphoxide and sulphone metabolites after oral administration of single or multiple dose(s) of > 350 mg of DuP 128 to healthy subjects.